Unstable intermediates. Part 205. Radical cations of pyrrole, furan, and thiophen derivatives: an electron spin resonance study

Abstract

Exposure of dilute solutions of pyrrole, 2,5-dimethylpyrrole, furan, thiophen, and 2,5-dimethylthiophen in Freon at 77 K to ⁶⁰Co γ-rays gave the corresponding cations. In all cases, analysis of their e.s.r. spectra established that the unpaired electron occupies the ¹a₂(π₃) orbital with a node through the heteroatom. Data for the dimethyl derivatives are close to those recently reported for the 1,3-dimethylcyclopentadienyl radical, whilst those for the unsubstituted radicals are similar to those for the radical cation of cyclopentadiene.